The present invention relates to a magnetic head, and more particularly to a magnetoresistive effect type magnetic head and a method of producing of the same.
A prior art magnetic head of the magnetoresistive effect type is shown in FIGS. 1 to 3. A plan view is shown in FIG. 1, a front side as viewed from a magnetic recording medium is shown in FIG. 2, and a side view thereof together with a magnetic recording medium is shown in FIG. 3. In these drawings, characters x, y and z show directions.
This magnetic head of the magnetoresistive effect type comprises a substrate 1 made of a soft magnetic material such as ferrite, Sendust or permalloy having a magnetic shield effect or a nonmagnetic material such as silicon or glass, a nonmagnetic insulating film 2 of SiO, SiO.sub.2, ZnO or Al.sub.2 O.sub.3 laid on the upper surface of the substrate 1, a hard permanent magnet film 3 made of an oxide magnetic material containing at least iron such as an oxide of the Fe-Co-Cu group or Co and a magnetic material of the Co-P group on the upper side of the nonmagnetic insulating film 2, a nonmagnetic insulating film 4 of a material such as SiO, SiO.sub.2, ZnO or Al.sub.2 O.sub.3 laid on the permanent magnet film 3, a plurality of elongated rectangular strips comprising a film 5 of the magnetoresistive effect type consisting of a ferro-magnetic film such as Fe-Ni or Fe-Al-Si exhibiting a magnetoresistive effect and a magnetic easy axis direction K along the longitudinal direction (direction z in FIG. 1), and conductive films 6 and 7 made of Au, Cu or Al at the longitudinal ends 5a and 5b of the film 5. A DC constant current i flows longitudinally in the magnetoresistive effect film 5 through the rear ends 6a and 7a of the conductive films 6 and 7. This magnetic head of the magnetoresistive effect type further comprises a nonmagnetic insulating film 8 of a material such as SiO, SiO.sub.2, ZnO or Al.sub.2 O.sub.3 on the magnetoresistive effect film 5 and the conductive films 6 and 7, and a protective substrate 9 of a nonmagnetic material such as glass or silicon or a soft magnetic material such as ferrite, Sendust or permalloy having a magnetic shield function laid, through a layer of a bonding agent such as epoxy resin or glass (not shown), on the film group including the nonmagnetic insulating film 2, the permanent magnet film 3, the nonmagnetic insulating film 4, the magnetoresistive effect films 5, the conductive films 6, 7 and the nonmagnetic insulating film 8 arranged sequentially as mentioned above. In FIG. 3, reference numeral 10 shows a magnetic recording medium such as a magnetic tape or a magnetic disc. Arrow A shows the direction in which the magnetic recording medium 10 travels, and characters N and S show the magnetic charges of the signal recorded in the magnetic recording medium 10. The magnetic head shown in FIGS. 1 to 3 is of the multi-element type in which a plurality of magnetoresistive effect films 5 and the like are arranged. Unlike this magnetic head, a single-element magnetic head including only one film is applicable with equal effect. In this magnetic head of the magnetoresistive effect type, films are formed by such techniques as deposition by evaporation, sputtering or electrodeposition, and a minute pattern is formed by use of the processes of photo-etching or electroforming.
Next, the operation of the magnetic head of the magnetoresistive effect type mentioned above will be briefly explained.
The magnetization Ms of the magnetoresistive element film 5 having a magnetic easy axis direction K coincident with the direction z is affected by the magnetic flux .phi. leaked from the signals recorded in the magnetic recording medium 10 traveling in the direction of arrow A (direction x) and thus is directed in a direction which is at an angle .theta. to the direction z to satisfy minimum energy conditions. As a result, the resistivity .rho. of the magnetoresistive effect element film 5 changes according to the formula. EQU .rho.-.rho..sub.o .alpha. cos.sup.2 .theta. (1)
where .rho..sub.o is the resistivity of the magnetoresistive effect element film 5 without any magnetic flux .phi..
By applying a DC constant current i from the longitudinal ends 5a and 5b of the magnetoresistive effect element film 5 in the longitudinal direction (in the easy axis direction K), a voltage change (output voltage e) may be measured across the longitudinal ends 5a and 5b of the magnetoresistive effect element film 5 in accordance with the recorded signal in the magnetic recording medium 10. This fact will be explained with reference to FIG. 4. In FIG. 4, the curve B.sub.1 represents a characteristic in the form of the relation between the magnetic flux .phi. (or applied magnetic field H) and the output voltage e. In view of the fact that this curve B.sub.1 includes a non-linear region, a predetermined bias DC magnetic field H.sub.b is applied to the magnetoresistive effect element film 5 so that the operating point is moved to point P thereby generating a recording signal shown by the curve B.sub.3 from the magnetic recording medium 10 having the characteristics shown by curve B.sub.2 in the linear region. The bias DC magnetic field H.sub.b is obtained by magnetizing the permanent magnet film 3 within the plane thereof.
The bias DC magnetic field H.sub.b applied to the magnetoresistive effect element film 5 from the permanent magnet film 3, on the other hand, depends to a large measure on the construction of the magnetic head of the magnetoresistive effect type. For example, assuming that the substrate 1 is made of a nonmagnetic material such as silicon or glass and that the magnetoresistive effect element film 5 is made of an alloy of 83% Ni and 17% Fe, namely, the saturation magnetic flux density Bs is approximately 10 K Gauss, then the residual magnetic flux density Br of the permanent magnet film 3 is required to satisfy the condition of the equation below. EQU Br.times.t.sub.h .gtoreq.10.sup.4 .times.t.sub.MR ( 2)
where t.sub.h is the thickness of the permanent magnet film 3 and t.sub.MR the thickness of the magnetoresistive effect element film 5.
In the case where this magnetic head of the magnetoresistive effect type has a magnetoresistive effect film 5 of the thickness t.sub.MR of 1000 A and a permanent magnet film 3 made of an oxide magnetic material of Fe-Co-Cu group having a residual magnetic flux density Br of 2000 Gauss, then the thickness t.sub.h of the permanent magnet film 3 is required to be EQU t.sub.h .gtoreq.10000/2000.times.1000=5000 A
The conductive films 6 and 7 laid on the longitudinal ends 5a and 5b of the magnetoresistive effect element film 5 and on the non-magnetic insulating film 4 are easily broken due to the existence of a step portion 3a of 5000 A or more of the permanent magnet film 3 positioned beneath the conductive films 6 and 7. This problem has not been solved completely. If the thickness t.sub.MR of the magnetoresistive effect element film 5 is increased in order to reduce the distortion, the thickness t.sub.h of the permanent magnet film 3 also increases, and the problem of the conductive film 6 being likely to be broken at the stepped portion 3a is aggravated. This problem of the risk of breakage becomes more serious in the case where the substrate 1 is comprised of such a soft magnetic material as permalloy or a ferrite of the Ni-Zn group or the Mn-Zn group. In other words, the conditions below are required of the permanent magnet film 3 instead of those defined by equation (2). EQU Br.times.t.sub.h .gtoreq.2.times.10.sup.4 .times.t.sub.MR ( 3)
In a manner similar to the preceding case, assuming that t.sub.MR =1000 A and Br=2000 Gauss, the thickness t.sub.h of the permanent magnet film 3 is given as EQU t.sub.h .gtoreq.2.times.10000/2000.times.1000=10000 A
ps From this, it will be seen that the problem of the risk of breakage at the stepped portion 3a becomes more serious.
If the substrate 1 and the protective substrate 9 of this magnetic head are both made of a soft magnetic material, the substrate 1 and the protective substrate 9 function as a magnetic shield member, so that reproduction at a short wavelength will be possible. The important factor for reproduction at a short wavelength by this construction is to reduce as far as possible the distance (hereinafter referred to as the gap) g between the magnetoresistive effect element film 5 and the substrate 1.
This gap is determined as explained below. Assume that the conductive film 6 is not broken even at 10000 A or more of the stepped portion 3a and that the thicknesses of the non-magnetic insulating film 2, the permanent magnet film 3 and the non-magnetic insulating film 4 are 4000 A, 10000 A and 1000 A respectively. Then the gap g is expressed as EQU g=4000+10000+1000=15000 A
The distance between the magnetoresistive effect element 5 and the protective substrate 9 is also called the gap, which is designed to be the same as the gap g. Specifically, assuming that the thicknesses of the conductive films 6, 7, the non-magnetic insulating film 8 and the bonding agent layer (not shown) are 2000 A, 12000 A and 1000 A respectively, the gap referred to above is given as EQU 2000+12000+1000=15000 A
which is the same as the gap g. Thus, if the minimum wavelength .lambda..sub.min making possible reproduction is about 2.multidot.g, .lambda..sub.min .apprxeq.2.times.1.5=3.0.mu.. It is thus impossible to satisfactorily reproduce the wavelengths shorter than 3.mu..
As mentioned above, the conventional magnetic head of the magnetoresistive effect type is such that if a required bias DC magnetic field is to be applied to the magnetoresistive effect element film 5, the permanent magnet film 3 under the magnetoresistive effect element film 5 is thickened thereby inconveniently posing the above-mentioned problem.